The transport of lipids in blood is mediated by the plasma lipoproteins. The mechanism involved in the formation of these protein-lipid complexes, as well as the detailed architecture of these molecules, remains obscure. These ongoing studies are directed toward reaching an understanding of the chemical nature of these particles. In particular, by a combination of chemical modification and enzymatic "surgery", the A-1 protein in HDL3 will be degraded and the peptides which possess a strong affinity for lipid will be separated from those which do not. Following purification and characterization of these peptide fragments, the lipid-binding and non lipid-binding regions of the A-1 amino acid sequence will be identified. It is expected that this information will allow critical evaluation of present hypotheses concerning the nature of these protein-lipid interactions, perhaps resulting in the formulation of new working models for these processes.